unit_symbol.h

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#pragma once
#include <array>
#include <ratio>
#include <string_view>
#include <type_traits>
 
namespace SI::detail {
 
template <char... Cs> struct unit_symbol_impl {
  static_assert(sizeof...(Cs) > 0, "Empty strings are disallowed");
  // using double curly braces to because of a bug in clang5
  // See https://bugs.llvm.org/show_bug.cgi?id=21629
  static constexpr const std::array<char, sizeof...(Cs)> value{{Cs...}};
  static constexpr const std::string_view str{value.data(), value.size()};
};
 
template <typename _ratio> struct ratio_prefix : std::false_type {};
 
template <>
struct ratio_prefix<std::atto> : std::integral_constant<char, 'a'> {};
template <>
struct ratio_prefix<std::femto> : std::integral_constant<char, 'f'> {};
template <>
struct ratio_prefix<std::pico> : std::integral_constant<char, 'p'> {};
template <>
struct ratio_prefix<std::nano> : std::integral_constant<char, 'n'> {};
template <>
struct ratio_prefix<std::micro> : std::integral_constant<char, 'u'> {};
template <>
struct ratio_prefix<std::milli> : std::integral_constant<char, 'm'> {};
template <>
struct ratio_prefix<std::centi> : std::integral_constant<char, 'c'> {};
template <>
struct ratio_prefix<std::kilo> : std::integral_constant<char, 'k'> {};
template <>
struct ratio_prefix<std::mega> : std::integral_constant<char, 'M'> {};
template <>
struct ratio_prefix<std::giga> : std::integral_constant<char, 'G'> {};
template <>
struct ratio_prefix<std::tera> : std::integral_constant<char, 'T'> {};
template <>
struct ratio_prefix<std::peta> : std::integral_constant<char, 'P'> {};
template <>
struct ratio_prefix<std::exa> : std::integral_constant<char, 'E'> {};
 
} // namespace SI::detail
namespace SI {
template <char _dimension_symbol, typename _ratio,
          typename _exponent = std::ratio<1>>
struct unit_symbol : public std::false_type {};
 
} // namespace SI